Light is the major limiting factor for intensive agriculture. Harnessing the light energy efficiently or developing the crop genotypes that yield better under low light is the need of the hour. However, due to non availability of easily quantifiable tool, the screening for shade tolerance has become complex. Hence, an attempt was made in this investigation to employ the Carbon Isotope Discrimination (Δ13C) as a physiological marker/tool in assessing the extent of shade tolerance in black pepper, as it has plant types differing in shade tolerance. On the basis of Photosynthetically Active Radiation (PAR), different shade levels of 50, 65 and 90 percent were created using shade nets. The growth and physiological parameters were measured periodically. Among the genotypes, the one which has relatively high adaptation to the shade has shown to utilize the light more efficiently thus maintaining low Ci, and hence the low Δ13C . It also maintained higher photosynthetic rate and lower transpiration rate. In this paper we discuss the physiological basis for this variation and currently we are contemplating to test the same hypothesis in other shade loving species too.